well i did originally pick marbles to sim a sniper rifle, hence why the barrel is so long the chamber originally so huge. But i bet no one has had a same diameter gun with equal sized chamber as my original idea.

Even if you make the barrel long enough to get a decent ratio flow will still be constricted like crazy. And at 120psi(the limits of pvc) there is no way that it will get supersonic without helium or other lighter gas, there just isnt enough 'push'.

Still a supersonic velocity isnt remotely possible until 400psi without a lighter gas.....Still it wont happen unless you have an extremly light projectile and a massively overkill barrel and chamber.
If you want to go supersonic then just make a hybrid.

Your wasting your money, but if you want to do that then I cant stop you.
And please instead of saying things like "comby", just take the time to type out the full word. Combustion, see it isnt so hard.
It took me like two minutes to figure out what you meant by "comby"

The material is simply too weak to hold the pressures needed for supersonic muzzle velocities.
If you still would want to achieve supersonic in pvc, it would require an enormous amount of of it if you are using low pressures, or use a pvc pipe with like 1" thick walls so it can hold those pressures, but then again, it becomes way too expensive, and metal would be a better option.

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Till the day I'm dieing, I'll keep them spuddies flying, 'cause I can!

bigbob12345 wrote:Even if you make the barrel long enough to get a decent ratio flow will still be constricted like crazy. And at 120psi(the limits of pvc) there is no way that it will get supersonic without helium or other lighter gas, there just isnt enough 'push'.

I'm pretty sure that says 280psi... OTOH, my sprinkler valve is definitely only rated to 120, but a well built piston gun... well that blows your statement out of the water...

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enough said...

"<I>For dare to be peace, I have to keep at it everyday, da Man doesn't take days off so neither can I</I>" -<B>Bob Marley</B>, day before a performance, a day after being shot in the chest. "<I>If you are the big, big tree, we are the small axe, ready to cut you down!</I>" -Bob again

You're saying that it's possible to break the speed of sound using plastic pipe, a pressure higher than that of which it was designed to hold, and you don't really know how you're going to do it.
You talking about these ridiculous propositions on an open community does not only jeopardize yourself, but any inexperienced (like yourself) people may pass through and take your word as safe. It's not ok to talk about unsafe ideas on an open forum.